Integrated processing of biomass and liquid effluents

ABSTRACT

An integrated process for the combined fermentation and the conversion of liquid and solid residues generated by the cane sugar industry into a variety of useful products. The process also relates to the treatment of other biomass materials. The process combines elements of alcohol-based organosolv pulping with fermentation in a fully integrated operation. This process eliminates the need for separate costly facilities, thus reducing capital and operating costs, providing opportunities for heat and energy reduction and a high degree of internal process recycle. The process would replace costly waste and residue treatment operations with revenue generating operations.

RELATED APPLICATIONS

[0001] Australian Patent Application No: 51888/00; Filing Date: Aug. 8,2000; Relationship: Equivalent claims

[0002] U.S. Provisional Patent Application No. 60/307,712; Filing Date:Jul. 26, 2001; Relationship: Equivalent claims

BACKGROUND OF INVENTION

[0003] This invention relates to a process for the manufacture ofmultiple valuable products from various wastes generated during theproduction and recovery of cane sugar, as well from other agriculturalcellulosic biomass materials.

[0004] The cane sugar industry generates vast quantities of liquidwastes and solid residues during the production of its primary product.These include sugar cane bagasse and liquor streams containing largequantities of low-grade sugars. Bagasse is usually burned inefficientlyin boilers to generate steam and power. The liquid waste streams, mostlymolasses, are usually sold as low-grade cattle feed additives.

[0005] The cane sugar industry is normally a highly competitive, lowprofit industry. One approach to improve profitability is to convertthese wastes and residues into saleable products that can add to therevenues of the industry. The value of this approach has been recognizedfor a number of years and considerable research and commercialdevelopment has been undertaken to identify useful products, such asfurfural and papermaking pulp that can be generated from these wastes.

[0006] A new type of pulping technology, known as organosolv pulping,has distinct advantages for the cane sugar industry. It has almost noenvironmental problems, is less capital intensive than kraft, itproduces multiple co-products, is ideally suited to pulping non-woodbiomass that contain high levels of inorganic materials, and can beprofitably operated on a much smaller scale than conventional pulpingprocesses. Organosolv pulping has been described in numerous patents andpublications including U.S. Pat. No. 3,585,104 Kleinert, U.S. Pat. No.4,100,016 Diebold et al., U.S. Pat. No. 4,496,426 Baumeister et al.Although organosolv pulping has numerous advantages over conventionalchemical pulping methods, such as the kraft, sulfite and the sodaprocesses, in the pulping of wood and other woody biomass resources, itsuffers from a disadvantage of significant losses of the relativelycostly organic solvent from the process. If the solvent employed isethanol the environmental consequences of this loss is minor, but theeconomic consequences can be important, since they can make theoperating costs of an organosolv process higher than those forconventional chemical pulping processes. This requires the provision ofsubstantial quantities of expensive make-up solvent to the process. Thishigher operating cost is one major reason that has held back thecommercial acceptance of organosolv pulping processes.

[0007] One approach to reducing the cost of make-up solvent required byan organosolv pulp mill, to make it economically attractive, is toproduce the required make-up solvent on site. For an ethanol-basedorganosolv pulp mill a fermentation facility can be constructed adjacentto the pulp mill for this purpose. However, if constructed on a smallsize sufficient for the make-up needs of a small pulp mill, the relativecapital costs of such a fermentation facility would make it economicallyunattractive. Furthermore, if the pulp mill uses wood as a raw material,the fermentation plant would need to purchase fermentation feedstock,such as sugar or starch, at considerable cost. This problem can beovercome for an ethanol-based organosolv pulp mill processingagricultural residues, such as bagasse. Such a pulp mill processingbagasse would ideally be situated adjacent to a cane sugar mill, sincethe bagasse is a low value product of these mills. Therefore notransportation costs would be incurred for the raw material. Another lowvalue by-product of the sugar mill is molasses, a high sugar contentliquid by-product. It is well recognized that molasses can be readilyfermented commercially to yield ethanol. It therefore represents a lowcost fermentation feedstock present at the sugar mill.

[0008] Even more attractive for the cane sugar industry is thatethanol-based organosolv pulping is highly compatible with anagricultural economy. Its primary process chemical is ethanol, which canbe easily produced by fermentation of waste sugars and starch.Furthermore, many of the co-products of the process find immediate useand value in agriculture, such as animal feed supplements and slowrelease fertilizer and pesticides. This invention solves the problem ofthe high capital cost of a dedicated small fermentation plant to providemake-up ethanol by physically integrating the fermentation of molassesinto the process equipment of an organosolv pulp mill. A single millconsisting of organosolv pulping of biomass residues integrated with theprocessing and fermentation of aqueous waste streams will result inmajor profits for the cane sugar industry. At the same time such astrategy will result in a high degree of environmental protection andsupport for the development of adjacent industrial activities based onthe co-products of this process.

BRIEF SUMMARY OF THE INVENTION

[0009] The present invention provides a process for delignifying biomassfibrous residues comprising digesting biomass fibrous residues in amixture of ethanol and water in a digester at elevated temperature andpressure.

[0010] The process would include the step of treating spent liquor torecover lignin, acetic acid, furfural, xylose and other co-products, aswell as recovering alcohol for re-use in the process and subjectingvarious liquid sugar waste streams of the process and from a cane sugarmill to fermentation in order to produce ethanol and other fermentationproducts which may be used in the process. The recovery of ethanol fromthe spent cooking liquors and the recovery of ethanol from thefermentation liquors would be accomplished in the same processequipment. These two processes, the organosolv pulping and thefermentation of waste sugar streams, would be accomplished in the sameplant, which would allow equipment, heat and energy integrationproviding considerable economic advantages. This process concept isapplicable to other biomass residues as well as cane-sugar residues. Thepotential advantages of integrating these two formerly separateactivities into a single operating unit are numerous. They include lowertotal capital costs, combining different liquor streams for commonproduct recovery, opportunities for process heat and energy reduction,internal process chemical production, reduced transportation costs,substantial environmental improvement and the potential for the use oflarger, more efficient equipment in a shared operation. Separatefacilities operating in isolation may not be economic. This identifiesthe unit processes and the product flows in an integrated total processthat would provide these advantages to the cane sugar industry.

[0011] The distillation tower in the process could recover not onlyethanol for recycle, but also furfural and ethyl acetate, two valuableproducts that are generated during the bagasse cooking stage. Both canbe sold, probably as crude products suitable for upgrading at acentralized facility. Such activities would encourage the formation ofadditional local industries designed to support the sugar caneprocessors using the technology described in this invention. Other localindustries could take the lignin produced in these mills and convert itto value-added products, such as concrete admixtures and dyedispersants. Other options presented by this invention include therecovery of xylose (a sugar present in large quantities, mostly asxylan, in bagasse). This could be sold in the world market for purexylose that is used as a starting material in the production of theanti-caries sweetener, xylitol. Xylose can also be converted tofurfural. If market prices support this option then xylose recoverycould be maximized by extended steaming of the bagasse prior to cooking.Xylose would be recovered from the steaming condensate.

[0012] Utilizing this invention could lead to higher value pulps whichwould have high alpha-cellulose content and therefore be suitable forrayon production. The result for the cane sugar industry of practicingthis invention would be the elimination of costly environmental controloperations and the production of significant revenues from the sale ofseveral value-added products. These products would in turn createopportunities for the introduction of ancillary industries.

DESCRIPTION OF THE DRAWING

[0013] In the accompanying drawing, which illustrates by way of examplethe embodiment of this invention,

[0014]FIG. 1 is a flow diagram identifying the unit process steps of anintegrated process for the production of pulp and several usefulby-products from bagasse, a biomass residue of the cane sugar industry.While not every unit process is essential for the economic success ofthe invention, the combination of all these unit processes providesmaximum utility of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0015] The present invention is directed at a single integrated processthat converts biomass residues from the cane sugar industry, sometimesreferred to as bagasse, into a series of valuable products including,but not limited to, papermaking pulps. The process is integrated withthe element of fermentation of waste and low-grade molasses to produceethanol, other fermentation products and high protein animal feed. Othersources of low grade, but fermentable carbohydrate may be substitutedfor molasses in this invention. A key element incorporated into theprocess is organosolv delignification of bagasse. This element utilizessome of the alcohol generated in the fermentation element. Theorganosolv element generates products such as lignin, xylose, furfural,acetic acid and pulp for use in papermaking, dietary fibre, or aschemical cellulose. Much utility is gained by integrating these severalelements into a single process. The advantages include heat and energyreduction through process integration, capital reduction through theco-processing of various process streams and waste minimizationopportunities through the combining of several process streams. Theseelements and advantages are illustrated in the process flow diagram,FIG. 1.

[0016] The process starts with the preparation of the bagasse into aform suitable for packing into a pressure vessel, identified in FIG. 1as a digester. The preferred form is into stem sections of approximatelyten centimeters in length, but any similar form is appropriate. Acompressed pellet is also appropriate as feed for the digester. Asillustrated the digester is one of a series of batch digesters that maybe rotating spheres, or a continuous conveyed inclined or horizontaltube configuration, but could also be a vertical tubular batch orcontinuous design. In FIG. 1 a preferred configuration of a rotatingglobe batch digester configuration is illustrated. The operationsdescribed below for one digester are identical to those for theadditional digesters that are operated sequentially at appropriateintervals to allow optimal use of the remaining equipment in theprocess.

[0017] Following preparation of the fibrous residue (bagasse) into theuseful form described above it is conveyed by conveyer, 41, to the topof the digester for loading into the digester. Once the digesters, isfilled with a pre-determined amount of bagasse, the conveyer is stoppedand the digester is closed. An exhaust valve, 46, located behind ascreen, 42, in the bottom of the digester is now opened and low-pressuresteam (less than 50 psi) is allowed to enter the top of the digesterthrough a pipe, 45. This steaming, which is required to displace air inthe fibre bed, continues until temperature sensors in the exhaust lineindicate that steam is exiting from the bottom of the digester. Anycondensate of the steaming exits through the same line. Alternatively,if the moisture content of the bagasse is too high, nitrogen gas may besubstituted for steam for the air displacement. All valves are nowclosed and the pump, 43, in the line exiting the 2^(nd) liquor tank isturned on. The 2^(nd) liquor tank is full of aqueous alcohol at thedesired concentration and temperature. This liquor was used as a washliquor from a previous digester cook and was retained between cooks inthe 2^(nd) Liquor Tank, 3. The preferred alcohol concentration in wateris in the range of 35%-70% (w/w) and the preferred temperature is in therange of 170°-205° C. This liquor is pumped through a heat exchanger,44, to maintain its desired temperature and then into the top of thedigester through the top liquor line. Once the digester starts to fill,liquor exits the bottom of the digester from behind a screen, 42,constructed around the outlet line at the bottom of the digester, fromwhere it is returned to the top of the 2^(nd) Liquor Tank, 3. This hotliquor circulation is continued for the appropriate time necessary toraise the contents of the digester to the desired cooking temperature.At this point the liquor exit valve, 46, is closed and the desiredweight of hot liquor, usually 2 to 5 times the dry weight of thebagasse, is Pumped into the digester from the 2^(nd) Liquor Tank. Liquorflow is then stopped, steam is continually sent to a jacket surroundingthe digester to maintain its temperature at the desired cookingtemperature and the globe digester is rotated for the desired cookingtime. This time is normally between 30 minutes and 3 hours, with thepreferred time being between one and two hours. At the end of this timethe rotation of the digester is stopped with the liquor outlet line andsurrounding screen at the bottom of the digester. Part of the hot blackliquor is then flashed into a Flash Tank, 6. The valve at the top of the2^(nd) Liquor Tank is then closed and the return liquor is diverted tothe Spent Liquor Tank. Residual liquor in the 2^(nd) Liquor Tank ispumped down to a level sufficient to keep the suction side of the pumpflooded. Liquor remaining in the Digester is drained through the lowerscreens into a drain line from where it is also pumped to the SpentLiquor Tank. Next, clean aqueous alcohol at the concentration andtemperature previously described is pumped from the 1^(st) Liquor Tank,2, into the top and bottom lines of the Digester and returned to the2^(nd) Liquor Tank, 3, using the appropriate valves and pumps. After the1^(st) Liquor Tank has been almost emptied liquor flow to the Digesteris stopped and the remaining liquor in the Digester is drained down andpumped to the 2^(nd) Liquor Tank through the appropriate lines andvalves. The Digester is now depressurized by opening the valves in thetop line and the vapors passed to a Blow-Down Condenser, 35. Thealcohol-rich vapors are condensed and returned to the Recovery AlcoholTank, 9, for re-use in the process. The partially-delignified fibres arenow sluiced from the Digester through the bottom valve, using water orpreferably condensate from the evaporator. This sluiced pulp is sent toa tank, 51, from which it is pumped continuously to conventional pulprefining, washing, screening, cleaning and bleaching operations. Theliquor from these operations can be processed by conventional means foralcohol recovery and sodium acetate recovery.

[0018] The spent liquor under pressure in the Spent Liquor Tank, 4, isflashed into a Flash Tank, 6, and the vapors condensed through theBlow-Down Condenser, 35, and returned to the Recovery Alcohol Tank, 9,for re-use. The condensed liquor in the Flash Tank, containing theextracted lignin, is then pumped to the Lignin Precipitation Tank, 7,where it is mixed rapidly with stillage from the Distillation Tower, 14,and the pH adjusted to below 3.0 with acid and the mixture cooled toabout 17°. Lignin precipitates from the mixture and forms a slurry. Thisis pumped to a suitable filtering device, such as a drum filter, 13,where the lignin is removed as a wet cake that is sent to an appropriatedrier, while the filtrate is pumped to a Recovery Feed Tank, 54. Fromthis tank the filtrate is pumped to an appropriately designedDistillation Tower, 14. Such a tower would have a lower steam strippingsection and an upper rectifying section, or be composed of two columnshaving these functions. In this tower alcohol, together with someesters, is recovered as an overhead condensate and returned to theRecovery Alcohol Tank for re-use in the process. Furfural, which ispresent in the filtrate, accumulates at one of the lower trays in therectifier section where it is drawn off, cooled and mixed with waterbefore being sent to the Decanter. The lower liquid phase in thedecanter is crude furfural, which is upgraded to merchant furfural in acommercially available system. The upper layer is aqueous alcohol, whichis passed back to the Distillation Tower to recover the alcohol bymixing with the tower feed stream. Steam to power the stream strippingsection is provided by Reboilers at the bottom of the tower.

[0019] Aqueous stillage from the bottom of the Distillation Towercontaining sugars, some lignin and minerals, is sent to an appropriatelydesigned multi-stage evaporator, 19, where it is concentrated to about25% solids. This concentrate is pumped to an Evaporator ConcentrateDecanter, 23, where a lower layer of oily lignin is recovered and dried.The upper aqueous layer containing xylose, xylans, other sugars andminerals, is sent to a commercially available xylose recovery unit, 24,for production of purified xylose. The effluents from this unit includewaste hexose sugars, which are passed to the fermentation operations foralcohol production, and an aqueous solution of minerals, which arereturned to the cane fields as fertilizer.

[0020] The aqueous condensate from the Evaporator is passed to acommercially-available solvent extraction unit, 21, such as thoseemploying tri-octyl phosphine oxide, (TOPO), for recovery of aceticacid, formic acid, furfural and ethanol as separate marketable products.The clean water that exits this unit is useful in the pulp washing andbleaching operations.

[0021] Molasses is used as the fermentation raw material in afermentation plant, 26, employing yeast to produce ethanol and otherfermentation products. This medium may be supplemented with additionalsugars from acid-hydrolysis products of waste cellulose, as required formaximum productivity. Additional minerals that may be required at thisstage can be supplied from the waste liquor stream of the xyloserecovery plant. After fermentation is complete in a sequential batteryof batch Fermenters, the beer is pumped to a Filter, 31, where yeast andother solids are removed and dried for sale as high-protein animal feedsupplement. The clarified beer is then passed to the Recovery Feed Tank,54, mixed with the filtrate from the Lignin Recovery Filter and pumpedto the Distillation Tower for recovery of ethanol and other components.

[0022] By this invention a range of valuable products is produced fromthe solid and liquid residues of the cane sugar industry.

What I claim as my invention is:
 1. An integrated process performingfermentation of low value (molasses) and waste sugars together with theconversion of biomass residues from the cane sugar industry (bagasse)for the production of multiple useful products. Such process combinesthe elements of alcohol-based organosolv pulping and ethanolfermentation into a single integrated process.
 2. A process, as in claim1, in which the useful products are any combination, or number, ofproducts including unbleached papermaking pulp, bleached papermakingpulp, high alpha-cellulose pulp, organosolv lignin, furfural, aceticacid, ethyl acetate, sodium acetate, xylose, xylan, butanol, acetone,high-protein animal feed, plant fertilizer, uronic acids and ethanol. 3.A process for delignifying biomass fibrous residues comprising,digesting biomass fibrous residues in a mixture of ethanol and water ina digester at elevated temperature and pressure, continually exposingthe mixture of ethanol and water to the fibrous residues in a suitabledigester, or by circulating the mixture of ethanol and water between thedigester and a holding tank for a time sufficient to at least partiallydelignify the biomass fibrous residues and form a pulp, draining themixture to a spent liquor tank at the end of the circulation time,causing the remaining liquor and partially delignified biomass totransfer from the digester to a blow tank by opening the valve to theblow tank.
 4. A process according to claim 3, wherein the processincludes the step of recovering lignin and other chemicals from themixture of ethanol and water contained in the spent liquor tank.
 5. Aprocess according to claim 3 or claim 4, wherein the mixture of ethanoland water in the digester is maintained at a temperature in a range from170 to 205° C.
 6. A process according to claim 5, wherein the pressurein the digester and the holding tank is maintained at a level sufficientto prevent the mixture of water and ethanol from vaporizing.
 7. Aprocess according to any one of claims 3 to 6, wherein the mixture ofethanol and water in the digester contains ethanol and water in a ratioin a range from 35% to 70% by weight ethanol to water.
 8. A processaccording to any one of claims 3 to 7, wherein the circulation time liesin a range from 30 minutes to 3 hours.
 9. A process according to claim8, wherein the circulation time lies in a range from 1 to 2 hours.
 10. Aprocess according to any one of claims 3 to 9, wherein the processincludes transferring the contents of the spent liquor tank to a flashtank to enable volatile material to evaporate thereby leaving alignin-rich condensed liquor, lowering the pH of the condensed liquor toa level below 3, diluting the condensed liquor with an aqueous streamand cooling the condensed liquor to cause lignin to precipitate from themother liquor and separating lignin from the mother liquor.
 11. Aprocess according to claim 10, wherein the process includes the steps ofdistilling the diluted mother liquor to recover ethanol and furfuraltherefrom leaving an aqueous stillage.
 12. A process according to claim11, including the steps of concentrating the aqueous stillage byevaporation, allowing a liquid lignin fraction to settle, removing theliquid lignin fraction from an upper layer of the aqueous stillagethereby leaving an aqueous layer containing xylose, xylan and othersugars.